Early Changes in Fluorine-18-FDG Uptake During Radiotherapy

The aim of this case study was to quantify metabolic changes in tumor tissue during and directly after external radiotherapy. We performed six FDG-PET scans of the neck in a patient with two lymph node metastases of a papillary thyroid carcinoma and an antigranulocyte antibody scintigraphy of the same region to assess the inflammatory reaction. The FDG-PET scans show an initial increase of tracer uptake in both metastases after application of 6 Gy followed by a slow but constant decline with increasing radiation dose. In the deep metastasis the FDG uptake returned to the initial level after 30 Gy total dose whereas the metabolic activity in the superficial lymph node remained high, even after 60 Gy total dose. The antigranulocyte scan demonstrated an intense inflammation in the latter metastasis. There is an initial enhancement in metabolism induced by irradiation which is measureable by FDG-PET. With increasing dose, the metabolic activity declines constantly. The additional inflammatory reaction might contribute to the glucose uptake in irradiated tumors.